The present invention relates to a thermal transfer sheet and more particularly to a thermal transfer sheet which can provide a black image having excellent color density and various types of fastness.
Proposals have hitherto been made on methods wherein various full-color images could be formed on paper or a plastic film by a thermal transfer system using a sublimable dye. In these methods, a thermal head contained in a printer is used as heating means which transfers, by heating in a very short time, dots of three primary colors or four colors of black in addition to the three primary colors to a thermal transfer image-receiving sheet, thereby reproducing a full-color image of an original using the dots of a plurality of colors. Further, a single color, such as black, may be transferred to a thermal transfer image-receiving sheet to reproduce a monochrome image having a high gradation.
In the above thermal transfer system, since a dye is used as a colorant, the image formed is very sharp and highly transparent, offering excellent color reproduction and gradation of intermediate colors. Therefore, the quality of the image formed is equivalent to that of images formed by the conventional offset printing or gravure printing, and it is possible to form high-quality color images or monochrome images comparable to full-color photographic images.
Conventional thermal transfer sheets, for a black image, used in the thermal transfer system, however, cannot provide an image having excellent color density and various types of fastness because three primary colors, i.e., yellow, magenta, and cyan are combined in an improper manner.